1. Field of the Invention
The present invention relates to an organic electro luminance display device, and more particular to the organic electro luminance display device in which the stress of a driving transistor may be deceased and the remaining image in a screen may be prevented.
2. Discussion of the Related Art
Since the organic electro luminance display device had been introduced using conjugate polymer such as poly-phenyl vinyl (PPV), the organic material such as the conjugate polymer has been study vividly. Further, this organic material can be applied in various applications such as a thin film transistor, a sensor, a laser, a photoelectric device, and an organic electro luminance display device.
In case inorganic electro luminance display device made of phosphors series, since the high driving voltage should be applied to operate the device, the power consumption may be increased. Further, since the inorganic electro luminance display device is made with vacuum evaporation process, the cost is increased and it is difficult to fabricate the large size device. In addition, there is a problem that it is impossible to emit blue color in the inorganic electro luminance display device.
Comparing with the inorganic electro luminance display device, the organic electro luminance display device has some advantages, for example, high emitting efficiency, simplified process capable of large size device, blue light emitting. In addition, the flexible display device can be manufactured in the organic electro luminance display device. Thus, the organic electro luminance display device has been extensively studied as the next-generation flat panel display device. In particular, the active matrix organic electro luminance display device has been introduced as the flat panel display device.
The active matrix organic electro luminance display device can be classified a voltage driving mode, a current driving mode, and a digital driving mode in accordance with the driving method.
The voltage driving mode organic electro luminance display device of the various driving mode is mostly used, since the data can be written in high speed and the driving IC similar with the commercial driving IC used for a liquid crystal display device can be used.
FIG. 1 is a view showing a pixel 1 of the related art organic electro luminance display device. As shown in FIG. 1, the pixel 1 of the organic electro luminance display device is defined by a gate line GL and a data line DL crossing each other and the power line is disposed parallel to the data line DL in the pixel 1. In the pixel, two thin film transistors (TFTs) T1 and T1 and an emitting unit OLED are formed. These TFTs T1 and T2 take a different role in the pixel 1. That is, the second TFT T2, which is a switching TFT, sinks a scan signal supplied through the data line DL and the first TFT T1, which is driving thin film transistor, supplies the excitation signal to the emitting unit through the power line PL when the switching TFT is switched on.
A storage capacitor Cstg is disposed between the gate and the source of the driving TFT T1 to store and maintain the driving voltage of the driving TFT T1.
Hereinafter, the operation of the related art organic electro luminance display device will be described in detail.
When the gate signal GATE of ‘high’ state is applied to the gate line GL, the switching TFT T2 is turned on and then the driving TFT T1 sinks the sink current from the data line DL. At this time, the current of same amount is supplied to the all pixel of the organic electro luminance display device, since the sink current from the date driving IC is identical.
Thereafter, when the gate signal GATE of ‘low’ state is applied to the gate line GL, the switching TFT T2 is turned off. At this time, the driving TFT supplies the current corresponding to the voltage charged in the storage capacitor Cstg into the emitting unit OLED to emit the light.
However, there are some problems in the related organic electro luminance display device as follow.
When the data signal is black, the driving TFT T1 is turned off. That is, when the voltage of 0V V applied to the gate of the driving TFT T1, the voltage is not supplied to the emitting unit OLED so that the black is displayed in the organic electro luminance display device. In case of the black data signal, however, the voltage having some amount, not 0V, is applied to the driving TFT T1 by the surrounding environment and the error of the parts of the organic electro luminance display device. Thus, it is difficult to display black in the organic electro luminance display device. In addition, in the related organic electro luminance display device, the life of the driving TFT T1 may be decreased because of the continuous stress thereto.
In the organic electro luminance display device, since only the positive voltage is applied to the driving TFT T1, the threshold voltage of the driving TFT T1 is shifted so that the brightness of the organic electro luminance display device is deteriorated and the life of the organic electro luminance display device is decreased. In addition, the storage capacitor is only charged with the positive voltage, not discharged. Thus, the life of the organic electro luminance display device is decreased by deterioration the storage capacitor Cstg and the ghosting is generated.